The present invention disclosed herein relates to a semiconductor device, and more particularly, to a hybrid laser diode.
The present invention has been derived from research undertaken as a part of the information technology (IT) development business by the Ministry of Information and Communication and the Institute for Information Technology Advancement of the Republic of Korea [Project management No.: 2006-S-004-02, Project title: silicon-based high speed optical interconnection IC].
A hybrid laser diode using silicon and a III-V group compound semiconductor receives attention as a light source for photonics technology combining optical technology with electronic device technology.
FIG. 1 is a sectional view of a typical hybrid laser diode.
Referring to FIG. 1, a buried insulating layer 12, a silicon layer 13, and a light emitting diode 42 are sequentially stacked on a substrate 11. At this point, a silicon-on-insulator (SOI) substrate 41 is used for the substrate 11, the buried insulating layer 12, and the silicon layer 13.
The light emitting diode 42 is formed by patterning a III-V group compound semiconductor substrate, and includes an n-type semiconductor layer 21, an active layer 22, and a p-type semiconductor layer 25, which are sequentially stacked. In more detail, the III-V group compound semiconductor substrate can be attached to the SOI substrate 41 through wafer bonding technology, and the p-type semiconductor layer 25 and the active layer 22 of the attached III-V group compound semiconductor substrate are patterned to expose the top surface of the n-type semiconductor layer 21. Therefore, a slab waveguide SW is formed as illustrated in FIG. 1.
On the other hand, before attaching the III-V group compound semiconductor substrate, the silicon layer 13 is patterned to form a channel waveguide CW, which has the narrower width than the slab waveguide SW and is disposed below the slab waveguide SW. The channel waveguide CW has the width narrower than that of the slab waveguide SW. Accordingly, a void region 99 exposing the buried insulating layer 12 and filled with air is formed around the channel waveguide CW.
According to a hybrid laser diode, an optical mode of laser generated in the light emitting diode 42 overlaps at both the channel waveguide CW and the slab waveguide SW. Accordingly, the optical mode is guided by the channel waveguide CW, and can be electrically pumped in the light emitting diode 42 at the same time.
On the other hand, a related hybrid laser diode has technical limitations such as large leakage current, low thermal stability, and high series resistance. In more detail, since the active layer 22 and the p-type semiconductor layer 24 constituting the slab waveguide SW are formed to occupy a large area, current for an operation of the light emitting diode can be dispersed. To resolve this current dispersion, suggested is a method of forming an impurity region 24 defining an active region in the active layer 22 and/or the p-type semiconductor layer 25 using an ion implantation technique. That is, the active region is formed in the active layer 22 and/or the p-type semiconductor layer 25 disposed between the impurity regions 24.
However, as is well-known, due to atomic collisions during an ion implantation process and a subsequent diffusion of atoms, spatial distribution of impurity concentration, which is implanted through ion implantation technique, is close to Gaussian distribution. That is, the impurity region 24 has a gradient of concentration. Accordingly, a boundary of the impurity region 24 may not be discretely defined in both a vertical direction and a horizontal direction.
The active region defined by the impurity region 24 is a place where light emitting phenomenon occurs and which is used as the slab waveguide SW. Therefore, the horizontal gradient of impurity concentration is a factor that deteriorates an optical characteristic of a laser diode. Additionally, due to the vertical gradient of impurity concentration, impurities may be diffused into the n-type semiconductor layer 21, and this may increase an electrical resistance of a current path of light emitting diode.
Furthermore, as described above, the void region 99 filled with air has a low thermal conductivity, and thus heat generated from the light emitting diode 42 may not be efficiently emitted. Since operational and optical characteristics of a laser diode are very susceptible to a temperature, these poor thermal emission characteristics may deteriorate product characteristics. Additionally, since the distance between the active region and an n-type electrode 31 cannot be reduced by the impurity region 24, a typical hybrid laser diode suffers from a high series resistance between the n-type electrode 31 and a p-type electrode 32.